Vulcanization of butyl rubber by 2, 6-di-(alkoxymethyl)-4-hydrocarbyl phenols



VULCALNIZATION OF BUTYL RUBBER BY 2,6-DI- -(ALKOXYMETHY L) 4 HY DROCARBYL PHE- NOLS Pliny .0. Tawney, Passaic, N. J assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey 7 NojDra wing. Application September 27, 1955 Serial No. 537,044

4 Claims. (Cl. 260-62) CH2OR' wherein R is a hydrocarbon radical (e. g., an alkyl, aryl,

aralkyl or cycloalkyl radical) and R'- is an alkyl radical which contains not more than four carbon atoms, and i The resulting vulcanlzates (B) a heavy metal halide. have remarkable resistance to oxidation and to, exposure to elevated temperatures, and they have other desirable physical properties. It was surprising to find that the stated dialkoxymethyl-phenolic compounds, in the presence of heavy metal halides, will produce such improved Butyl rubber vulcanizates, because it has formerly been thought necessary, to have methylol groups on the phenolic nucleus in order to vulcanize Butyl rubber. The unexpectedness of the results obtained with the present vulcanizing system is further emphasized bythe fac't'that the described dialkoxymethyl-phenolic compounds will not vulcanize Butyl rubber in the absence of the heavy metal halide. Butyl rubber cured by this new method is superior in several important properties to Butyl rubber cured by the corresponding dimethylol phenol fanda.v

metallic halide.

1 PitCd ta e Pat n the copper on the Butyl rubber. The heavy metal ch10"v Butyl rubber, or GR-I, is a generic name for any of the well known synthetic rubbery copolymers of an iso-" olefin with a minor amount of a conjugated diolefin.

The isoolefins used generally have from 4 to 7 carbon atoms, and such isomonoolefins as isobutylene and 2 methyl-Z-buterie are preferred. The diolefins used have from 4 to 8 carbon atoms.

pip'erylene; 2,3-dimethylbutadiene; 3-methyl-L3-pcntadiene; 2-methyl-1,3-pentadiene; 1,3-hexadiene and,2,4-

hexadiene. The Butyl rubber typical contains from about 0.5 to 5%, and seldom-more than 10%,of copolymerized diolefin on the total weight of the elastomer. This relatively small amount of unsaturation renders the be-' havior of Butyl rubber toward vulcanizing agents fundamentallyv different from the behavior of the more highly unsaturated rubbers, such as natural rubber or GR-S, and therefore experience with such highly unsaturated rubbers afiords no basis for predicting the behavior of Isoprene and butadiene are I the most important of these diolefins; others. are

, iron and zinc.

we. I

phenol; 2,6-di(propoxymethyl)-4-tert-butylphenol; 2,6-di-;

(isopropoxymethyl)-4-tert-butylphenol; andj 2,6-di(nbutoxymethyl)-4-tert-butylphenol. v t

' The amount of 2,6-di(alkoxymethyl)-4-hydr0carbyl phenol employed in the invention usually rangesfrom about 2 parts (-by weight) to about 12 parts per parts of the Butyl rubber. .In general, aepreferred range of dialkoxymethylphenol curing agent is from about .4 parts to 8 parts perlOO of the rubber. The heavy metal halide-which may be regarded, as a kindof catalyst or activator or curing supplement, since the dialkoxymethylphenol itself will not .cure the Butyl rubber-is usually used in amount of at least 0.5 part, and I preferably use about 1 to 3 parts, per 100 parts of the Butyl rubber. Although in some cases even larger amounts of the metal halide can be used, say -10 parts, it is not generally necessary or desirable tense appreciably more than about 5 parts. In the majority of customarily use a large amount of the heavy metalhalide, e. g., from 5 to 10 parts, when I wish to cure the Butyl very rapidly at a low temperature, e. g., 100 C.

The heavy metal halides employed are exemplified by such known stable acidic halides as tin chloride, zinc chloride, iron chloride, and, in general, halides of the various metals usually classified as heavy metals (cf. the periodic chart of the elements in Introductory College Chemistry by H. G. Deming, published by John Wiley and Sons, Inc.). This class includes, inter alia, chromium chloride and nickel chloride, as well as cobalt chloride, manganese chloride and copper chloride. Although the copper halides may be used, I prefer not .to use them because of the possible deleterious effect of rides constitute the preferred class of activators or vulcanization adjuvants, although the heavy metal salts of other halides including bromine, fluorine, and iodine (such as stannic iodide) may also be used. Of 'the heavy metal chlorides, the most preferred are those of tin, The heavy metal halides are efiective independently of the state of oxidation of the metal, and they are even efiective if the halide is partially bydrolyzed, or is only a partial halide, as'in zinc oxychloride.

In carrying out the invention, the Butyl rubber, the 2,6-di(-alkoxymethyl) 4 hydrocarbylphenol, and the heavy metal halide, and any additional desired ingredients, may be mixed together in any desired order according to the procedures ordinarily used in mixing rubber compounds, with the aid of the usual rubber mixing equipment, such as an internal mixer or a roll mill.

The vulcanizable mixture resulting from the foregoing. ingredients may be fabricated into the desired'form by.

the usual methods, such as calendering, extrusion, or" molding, and subsequently vulcanized by heating, pref erably while confined under pressure.

Preferably carbon black is present in the productsf made by the process of this invention. As is we llknown,

similarly cured gum Butyl rubber. This improvement" likewise is conferred by carbon black on, Butyl rubber Patented Apr. 1, '1958' which is cured by the method of this invention. However, for certain products this improved tensile strength, etc., is not needed. Therefore, in its broadest aspect this invention relates to the cure of gum Butyl rubber and to Butyl rubber which contains other fillers, e. g., clays, titanium dioxide, etc., aswell as to black-filled Butyl rubber. i

The cure is conveniently carried out at temperatures of 100" C. or more, and preferably at temperatures in excess of 150 C., for periods of time ranging from about minutes to 3 hours, the longer periods of time Within the stated time range being employed with the lower temperature. The mostpreferred curing temperatures are within the range of about 160 C. to 190 (3., although somewhat higher temperatures may be employed, e. g., 200 to 205 C., provided that such high temperatures are not maintained long enough to cause thermal injury to the article. The time and temperature chosen for a particular cure not only are related inverse- 1y to each other but also are dependent on the amount of catalyst used. Therefore, the time and temperature of cure can be given only in the broad ranges shown above. Any skilled rubber compounder can easily determine conventionally the proper curing conditions for any particular stock.

The process of this invention is useful in making cured Butyl rubber products which resist aging at high temperatures in steam and/or air extremely well. Typical products are curing bags, steam hose, gaskets for equipment which must remain, at high temperatures continuously or intermittently for long periods of time, belts, inner tubes, tires, motor mountings, flexible hot air ducts, hot water bottles, etc. The cured products may also be phenyl acetate. The acetic acid formed in the reaction and the excess acetic anhydride are evaporated in high vacuo. The residue, without further purification, is treated with an excess of sodium hydroxide dissolved in the appropriate alcohol in the presence of a small amount of water, for several days at room temperature. The

2,6-di(alkoxymethyl)-4-hydrocarbylphenol so formed is isolated by fractional distillation in vacuo. My preferred vulcanizing agent, 2,6-di(methoxymethyl)-4-tertbutylphenol, boils at 90 C. at 0.03 mm. Hg has a refractive index (11, of 1.5113, and melts at 17 C. It will be understood that any and all of the vulcanizing agents employed in the invention may be prepared by the foregoing procedure, starting with appropriate corrcspending known materials.

The following example illustrates the invention. All parts are by weight.

Example A masterbatch was mixed on a rubber mill in the proportion of 100 parts of GR-I (a copolymer of isobutylene2isoprene, 98:2, according to Rubber Age 74, 561 (1954)), parts of carbon black, 2 parts of stearic acid and 5 parts of Indopol H300 (a commerciab ly available polybutene sold as a plasticizer for rubbers). Stannous chloride dihydrate and 2,6-di(methoxymethyl)- 4-tert-butylphenol were then mixed with individual portions of the masterbatch on the mill to form a series of stocks which diifered among themselves only in the amount of the curing agent. Portions of these stocks were cured in 6" x 6" x 0.1" molds under pressure at 161 C. (322 F.) for the individual times shown. The stocks then were tested conventionally, as shown, to determine the extent of cure and resistance to aging.

Stock 1 2 3 4 Masterbateh 157 157 157 157 SnCi JH O 1. 8 1. 8 1. 8 1.8 2.6-D1(methnxymethy1)4-tert-butylphenol 2 4 6 8 Cure (min.)

Green Tests:

it 1158 t d H58 '3 1 Tensile strength (P- L) 6O 00 1. 79 840 120 1, 640 1, 730 1, 940 1, 850 a a a as a Elongation (percent) 60 310 370 440 120 340 280 320 550 1 it it h h 1 Modulus (p. s. i.) 60 230 300 250 Aging Tests (60-minute cures):

Tensile Strength (p. s. i.)-

green 1, 490 1, 600 1, 790 1, 840 aged 3 days in steam a-.. 1, 290 1, 420 1, 660 1, 620 aged at hrs. in air b 1, 120 1, 530 1, 350 1, 3110 aged 48 hrs. in air 860 1, 330 1,310 1, 250 Elongation (percent)- green 380 310 370 440 aged 3 days in steam. 290 190 230 240 aged 24 hrs. in aha- 260 100 80 aged 48 hrs. in air 300 140 1'10 100% Modulus (p. s. i.)-

green 230 300 2:10 230 aged 3 days in steam. 290 420 440 410 aged 24 hrs. in air-.. 270 700 aged 48 hrs. in aha--- 230 950 950 =All steam aging tests were made at 164 C.

(85 p. s. i. of steam All air aging tests were made at 177 C. with air circulating throughout the test.

This example shows that 2,6-di(alkoxymethyl)4-tertbutylphenols cure Butyl rubber in the presence of staunous chloride, and that the cured products resist aging in steam and air extremely well.

Having thus described my invention, what I claim and desire to protect by Letters Patent is: p

1. A method of vulcanizing a synthetic rubbery c0- polymer of an isoolefin having from 4 to 7 carbon atoms with from 0.5 to 10% of a conjugated diolefin having from 4 to 8 carbon atoms, comprising heating 100 parts by weight of the said rubber at a temperature of from 100 C. to 205 C. for from 5 minutes to 3 hours, in admixture with (A) from 2 to 12 parts of a 2,6-di- (alkoxymethyl) -4-hydrocarbylphenol, wherein the said hydrocarbyl is selected from the group consisting of alkyl, aryl, aralkyl and cycloalkyl radicals, and wherein each alkoxy group contains no more than four carbon atoms, and (B) from 0.5 to parts of a heavy metal halide.

2. A method of vulcanizing a synthetic rubber copolymer of isobutylene with from 0.5 to 10% of isoprene, comprising heating 100 parts by weight of said rubber at a temperature of from 150 C. to 205 C. for from 5 minutes to 3 hours, in admixture with from 4 to 8 parts of 2,6-di(methoxymethyl)-4-tert-butylphenol and from 1 to 5 parts of a heavy metal chloride.

3. An improved vulcanizate characterized by resistance 7 6 of a 2,6-di(alkoxymethyl)-4-hydrocarbylphenol, wherein the said hydrocarbyl is selected from the group consisting of alkyl, aryl, nralkyl and cycloalkyl radicals, and wherein each alkoxy group contains no more than four carbon atoms, and (B) from 0.5 to 10 parts of a heavy metal halide.

4. An improved vulcanizate characterized by resistance to oxidation at elevated temperatures comprising parts by weight of a synthetic rubbery copolymer of isobutylene with from 0.5 to 10% of isoprene, vulcanized with from 4 to 8 parts of 2,6-di(methoxymethyl)- 4-tert-butylphenol and from 1 to 5 parts of a heavy metal chloride.

References Cited in the file of this patent UNITED STATES PATENTS 2,726,224 Peterson et al. Dec. 6, 1955 OTHER REFERENCES Van der Meer: Rubber Chem. Tech., 18, pages 

1. A METHOD OF VULCANIZING A SYNTHETIC RUBBERY COPOLYMER OF AN ISOOLEFIN HAVING FROM 4 TO 7 CARBON ATOMS WITH FROM 0.5 TO 10% OF A CONJUGATED DIOLEFIN HAVING FROM 4 TO 8 CARBON ATOMS, COMPRISING HEATING 100 PARTS BY WEIGHT OF THE SAID RUBBER AT A TEMPERATURE OF FROM 100*C. TO 250*C. FOR FROM 5 MINUTES TO 3 HOURS, IN ADMIXTURE WITH (A) FROM 2 TO 12 PARTS OF A 2,6-DI(ALKOXYMETHYL)-4-HYDROCARBYLPHENO, WHEREIN THE SAID HYDROCARBYL IS SELECTED FROM THE GROUP CONSISTING OF ALKYYL, ARYL. ARALKYL AND CYCLOALKYL RADICALS, AND WHEREIN EACH ALKOXY GROUP CONTAINS NO MORE THAN FOUR CARBON ATOMS, AND (B) FROM 0.5 TO 10 PARTS OF A HEAVY METAL HALIDE. 